A common technique for the distribution of DC power to large, multi-component computer systems or electronics systems is to provide a common power rail. (The term "rail," as used herein, includes both the hot path and return path.) This rail can be energized with DC power with a minimum number of connections to a power source yet can supply power to as few or as many components or units as the system requires. The impact of any interruption of the power to the rail during operation, however, can be substantial.
Various systems have been developed to render the power supplied through a common rail more reliable or fault tolerant. The power distribution system can include batteries. In the event of an interruption in the supply from the power source, the batteries can energize the rail for a sufficient period of time to permit an orderly shutdown or even to maintain reduced operation for a limited period of time. Redundant rails may be provided, each of which is separately powered, either from a separate power source or from batteries. In the event of an interruption of the power supply on one rail, power can be drawn from the other rail. Finally, even in a single rail system, that rail may be provided with power from more than one source. Thus, that rail will remain energized even should one of the power sources fail.
Two fault tolerant power distribution systems for computer systems are particularly relevant here. These systems both employ two rails, with power provided by 1,500 watt, 58 volt DC bulk power supplies. The computer system requires approximately 3,000 watts of DC power, at between 52 and 58 volts. Hence, two bulk power supplies are used in parallel.
In the first system, referred to as "N+1," the first rail is powered by two bulk power supplies to provide the 3,000 watt system requirements, plus a third bulk power supply to provide fault tolerance. All three bulk power supplies, in turn, draw power from an AC power distribution unit ("PDU") connected to a conventional AC power source. The second rail is powered by three batteries. As with the bulk power supplies, two batteries would be sufficient to meet the power requirements of the system. The third battery merely provides additional fault tolerance.
In the event any one of the three bulk power supplies fails or is taken out of service, the remaining bulk power supplies can meet system requirements. Should two or more bulk power supplies be unavailable, or AC power to the bulk power supplies is interrupted, system components can draw power from the second, battery-powered rail without any interruption in operation.
In the second power distribution system, a pair of the same bulk power supplies provide 3,000 watts of power to the first rail. A second pair of bulk power supplies provides power to the second rail. Each pair of bulk power supplies draws power from a separate PDU. In addition, each rail is also associated with a pair of batteries. This power distribution system is sometimes referred to as a "2N" system.
The 2N power distribution system provides even greater fault tolerance than the N+1 system. Either PDU can fail or be taken out of service. Even if AC power is interrupted completely, both rails remain energized by their separate batteries. In addition, the redundant pairs of bulk power supplies provides great flexibility and fault tolerance.
It sometimes occurs, however, that customer demand or changing conditions dictate that an N+1 system should be upgraded to a 2N system or that the protections of a 2N system are no longer required. The current invention permits such conversion between power distribution systems of varying degrees of fault tolerance and operational availability quickly, easily, and cost-effectively.